1. Field of the Invention
The present invention relates to method and apparatus for the nondestructive determination of torsional breakage torque of tubular carbon fiber reinforced composite materials (referred to subsequently as tubular CFRC materials), such as, for example, the inspection of a CFRC material shaft at the time of fitting to a golf club to determine whether or not defects exist in the shaft. The present invention also relates to method and apparatus that can be used in the quality control of tubular CFRC materials, or products utilizing such materials.
2. Description of the Related Art
With carbon fiber, in particular with tubular composite materials utilizing carbon fiber which has a high elasticity, it is known that the physical properties of the tubular composite material can show a significant drop from the design value when defects such as broken strands occur as a result of faulty conditions at the time of manufacture.
These kinds of defect are likely to occur, particularly when manufacturing by the sheet lapping process, and in this case, it is generally not possible to detect the defect from the external appearance
Consequently, conventional inspection methods involve those wherein the tubular composite material is destroyed and the failure strength measured. With these methods, since all of the test pieces are necessarily destroyed, it is not possible to test all products.
In view of the above, the present inventor previously filed a patent application (Japanese unexamined patent publication No. 5-107231) related to a defect detection method for tubular CFRC materials utilizing an eddy current flaw detection method.
Conventionally, eddy current flaw detection methods are widely used for the inspection of metal tubes. With these methods, output signals corresponding to defect locations such as locations A-E shown in FIG. 27, are obtained by comparing relative conditions between two adjacent points. Hence, signals a.sub.1 to e.sub.1 are output only at the starting point (suffix 1), and signals a.sub.2 to e.sub.2 are output only at the finishing point (suffix 2) of a flaw or defect. In the case of a continuous defect, an accurate assessment of the flaw condition is therefore not possible. This proves an obstacle to the improvement in inspection accuracy for tubular CFRC materials.